You don’t have to walk away, you can migrate.
We tried that with Lemmy and many great communities only have one or two people posting consistently.
Most people don’t care about behind the scenes
It depends, if mods were fully onboard and had a plan it definitely works. Just look at Piracy or Star Trek communities.
And look at the ttrpg.network community for a counterexample, they still have a pinned post on the dndmemes subreddit advertising Lemmy and ttrpgmemes gets like .1% of the traffic dndmemes does. And this is still after a months-long rebellion complete with allowing NSFW and restricting submissions to a single user account, both things that would normally kill a subreddit dead.
I just checked the Star Trek community on reddit and it’s still up with 753k members and 189 online. The Lemmy versions I can find are a fraction of that.
The idea of Lemmy is great but let’s not fool ourselves into thinking big communities actually migrated.
Depends on what your standard is, to me a community on here having 100+ daily users is already a huge success. I don’t think people expect the whole subreddit to migrate, just enough to have roughly the same amount of content/interaction.